Sinusoidal fluid tube



1956 G. v.- WOODLING ,732,863

SINUSOIDAL FLUID TUBE Filed Dec. 2. 1950 IVEGA TIVE l7 INTERNAL ALTITUDEAMP! AMPJTUDE 250a INTERNAL ALTITUDE INTERNAL ALTITUDE IN VEN TOR.

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United States Patent SINUSOIDAL FLUID TUBE George V. Woodling,Cleveland, ()hio Application December 2, 1950, Serial No. 198,856

1 Claim. (Cl. 138-47) My invention relates in general to tubing and moreparticularly to tubing used for hydraulic or fluid circuits.

With the modern trends of using higher pressures in hydraulic circuits,there is a growing difliculty of manufacturing hydraulic tubing whichwill withstand the vibration incident to fluid pressureshocks andmechanical shocks. The tube vibrations caused by peak fluid pressureshocks is in addition to the vibrations which are normally caused bymechanical shocks resulting from the relative movement o1 quivering oflocalized parts of the machine such as pumps, cylinders and valvesbetween which the hydraulic tubing extends. The total elfect of thesevibrations tends to cause leakage of the hydraulic fluid at the pointsof connecting of the tubing to the tube couplings or fittings mounted inthe hydraulic equipment. It has been found that this leakage may bereduced somewhat by clamping or otherwise securing the hydraulic tubingto the machinery or hydraulic equipment so that the amplitude of thevibrations of the tubing is held within close limits. However, there aremany installations in which it is extremely diflicult or awkward toclamp the tubing to the hydraulic equipment without encountering aconsiderable amount of expense.

In many instances in the installation of hydraulic tubing, it becomesengineeringly essential that the hydraulic tubing make a direct orstraight run instead of an indirect run between two points ofconnection; namely, the two points where the ends of the tubing areconnected to the tube fittings. In ordinary installation work, it ishighly recommended that the straight run be avoided because fromexperience it has been found that when a tubing is installed as astraight run between two points of connection, the possibility ofleakage at the tube fittings is greatly aggravated. One reason why astraight run produces an aggravated situation is the fact that thetubing through which the hydraulic oil flows is exposed to a differenttemperature than the base or other parts of the hydraulic equipment suchas the pumps, valves and cylinders. The mechanical strains in a director straight run tubing incident to expansion and contraction of thetubing caused by this change or diflerence in temperature must berelieved at some point which usually takes place at the tube fittings orcouplings where the ends of the straight run tubing are anchored to thehydraulic equipment. Another reason why the installation of a straightrun tubing gives aggravated trouble is that the hydraulic equipment suchas the pumps, cylinders and valves, to which the two ends of thestraight run tubing are anchored, are exposed to independent mechanicalshocks or quivering so that mechanical strains are transmitted to thepoints of connection of the tubing at the hydraulic tube couplings.Themechanical strains which are set up in the straight run tubing,regardless of whether it is-caused by the expansion and contraction dueto temperature changes or to the mechanical strains caused by mechanicalshocks or quivering of localized parts of hydraulic equipment, result inthe same trouble; namely, leakage at the tube conplings where the tubingis anchored to the hydraulic equipment.

An object of the present invention is to construct a hydraulic or fluidtube of such configuration that the tube will compensate for changes inthe contraction and expansion incident to changes in temperature and tomechanical shocks or quivering which may be set up in the localizedparts in the hydraulic equipment.

Another object of the invention is the provision of constructing ahydraulic or fluid tube of such configuration that the tube need not beclamped or otherwise secured to the parts of the hydraulic equipment inorder to dampen vibrations caused either by fluid peak shocks or bymechanical shocks or quivering.

Another object of the invention is the provision of constructing ahydraulic or fluid tube of such configuration that the internalresistance to the flow of the fluid is not appreciably increased.

Another object of the present invention is the provision of constructinga hydraulic or fluid tube of such configuration that it may be safelyand satisfactorily employed as a straight run between two couplingpoints.

Another object of the invention is the provision of a hollow sinusoidaltube having physical structure means residing within minimum and maximumlimits of sinusoidal amplitude and of longitudinal pitch.

Another object of the invention is the provision of constructing ahollow tube in an alternate series of straight and curved path sections.

Another object of the invention is the provision of constructing ahollow tube in a curved or substantially sinusoidal path sectionterminating at its opposite ends in straight path portions.

Other objects and a fuller understanding of my invention may be had byreferring to the following description and claim, taken in conjunctionwith the accompanying drawing, in which:

Figure l is a side view illustrating a short tube constructed in theform of a wavy or substantially sinusoidal body embodying my inventionand employed as a direct or straight run between two hydraulic units,such, for example, as between a pump and a cylinder, the ampli-- tude ofthe wavy body being substantially equal to the wall Figure 3 is an endview of the wavy or substantially diameter;

Figure 2 isa side view of an extended or long tube con-- structed in theform of a wavy or substantially sinusoidal? body from which the shorttube in Figure 1 may becut;

Figure 3 is an end view of the wavy or substantially sinusoidal tubeshown in Figure 2, looking from left to) right;

Figure 4 shows a series of cross-sectional views of the: Wavy orsubstantially sinusoidal tube for a section length of one pitch, thecross-sections being taken at intervals. of 45 degrees, ranging fromzero to 360 degrees, with the view at zero degree being an end view;

Figure 5 shows a modified form of the tube comprising an alternateseries of straight sections with an intermediate wavy or substantiallysinusoidal section therebetween of two pitch lengths, the amplitude ofthe wavy sections being substantially equal to one-half the diameter ofthe tube which has a one-quarter inch outside diameter;

Figure 6 is an end view of the tube shown in Figure 5, looking from leftto right;

Figure 7 shows a second modified form of the tube comprising analternate series of straight sections with an intermediate Wavy orsubstantially sinusoidal section therebetween of one pitch length, theamplitude of the wavy sections being substantially equal to one-half thediameter of the tube which has a one-quarter inch outside diameter; a

Figure 8 is an end view of the tube shown in Figure 7, looking from leftto right;

Figure 9 shows a further modified form of the tube comprising analternate series of straight sections with a one-half pitch wavy orsubstantially sinusoidal section therebetween, and one-half pitchsections appearing on opposite sides of the longitudinal axis of thetube;

Figure 10 is an end view of the tube shown in Figure 9, looking fromleft to right;

Figure 11 shows a further modified form of the tube comprising analternate series of straight sections with a one-half pitch wavy orsubstantially sinusoidal section therebetween, the one-half pitchsections appearing on the same side of the longitudinal axis of thetubing;

Figure 12 is an end view of the tube shown in Figure 11, looking fromleft to right;

Figure 13 is a further modified form of the tube comprising an alternateseries of straight sections with a wavy or substantially sinusoidalsection of one-quarter pitch therebetween; and

Figure 14 is an end view of the tube shown in Figure 13, looking fromleft to right.

My invention, which comprises a new tube construction, is shown inFigure 1 as being installed as a short straight run between twohydraulic units such, for example, as between a hydraulic pump 10 and ahydraulic cylinder 11 which may be mounted in spaced relationship withrespect to each other upon a common base 12 by means of stud bolts 13.The short tube in Figure 1, which comprises one form of the invention,is identified by the reference character 15 with each end thereofconnected respectively to the ptunp 10 and the cylinder 11 by means ofhydraulic tube fittings 14, which may be of any standard type. Ininstallation, the short tube 15 may be cut 01f the end of an extended orlong tube 16, such as shown in Figure 2, the lateral line 17 indicatingthe place of the cut. In mounting the tube 15 between the two hydraulicfittings 14, one or both of the hydraulic units; namely, the pump or thecylinder, may be dis mantled or loosened from the base by removingthestud bolts 13 so that the ends of the tube may be inserted endwise intothe hydraulic couplings, after which the hydraulic units are then firmlysecured to the base 10 by tightening the stud bolts 13.

The various pieces of short tubes which are required for a hydraulicinstallation are cut or fabricated from a long or extended tube, thetube 15 being an example of such a short tube. The long tubes, such as16, may be formed in substantially a sinusoidal wave at the mill orpoint of manufacture and then shipped to the place of installation wherethey are cut into short pieces to fit the hydraulic equipment. Forhydraulic installations, the commercial standard tubes usually begin atonequarter inch outside diameter and extend to one and one-half inchesoutside diameter, the diameters generally increasing from one-quarterinch to one inch at intervals of one-eighth inch and above one inch atintervals of one-quarter inch.

In this application, the following definitions apply:

Longitudinal axis is the true axis of a straight tube before it issinusoidally formed and is identified as the straight line in Figure 2to which arrow points that extend from legend: Longitudinal axis.

Sinusoidal axis is the real axis of a sinusoidal tube and is identifiedas the line in Fig. 2 which crosses the longitudinal axis at alternateintervals.

Sinusoidal amplitudeis a measure of the peak deviation or maximumlateral distance between the sinusoidal axis and the longitudinal axisand is identified in Fig. 2 as the lateral distance between the opposingarrows of which the upper arrow extends from the legend: Amplitude.

Minimum sinusoidal amplitude of a tube is present when the sinusoidalamplitude is approximately equal 4 to the wall thickness of the tube,and such a tube is illustrated in Fig. 2.

Maximum sinusoidal amplitude of a tube is present when the sinusoidalamplitude is approximately equal to one-half the outside diameter of thetube, and such a tube is shown in Fig. 5.

Negative internal diameter of a sinusoidal tube is a measure of thelateral distance between the longitudinal axis and the outside diameterof the tube and is identified in Fig. 2 as the lateral distance betweenthe two arrows bearing the legend: Negative internal diameter.

Zero internal diameter of a sinusoidal tube is present when the lateraldistance between the longitudinal axis and the outside diameter of thetube is zero and such a tube is shown in Figs. 5 and 6.

Longitudinal pitch of a sinusoidal tube is a measure of the longitudinaldistance between two corresponding points on the sinusoidal axis and isidentified in Figs. 2 and 7 as the longitudinal distance between the twoarrows bearing the legend: 1 pitch.

Lower limit of longitudinal pitch for tube with minimum sinusoidalamplitude is not less than approximately 4 times the outside diameter ofthe tube for all diameters of tubing.

Upper limit of longitudinal pitch for tube with mini mum sinusoidalamplitude is not greater than approximately twice that of the lowerlimit of longitudinal pitch.

First range of longitudinal pitch includes the values between the lowerand upper limits of longitudinal pitch for minimum sinusoidal amplitude.

Lower limit values of longitudinal pitch for tube with maximumsinusoidal amplitude is not less than approximately 5.5 times theoutside diameter of the tube for 4 inch tube; 6.0 for inch tube; 6.0 for/2 inch tube; 5.8 for inch tube; 5.8 for inch tube; 5.8 for inch tube;6.5 for 1 inch tube; 6.6 for 1% inch tube; and 7.0 for 1%. inch tube.

Upper limit values of longitudinal pitch for tube with maximumsinusoidal amplitude is not greater than approximately twice that of theupper limit values of longitudinal pitch.

Second range of longitudinal pitch includes values between the lower andupper limit values of longitudinal pitch for maximum sinusoidalamplitude.

In my invention, the value of the amplitude of the wavy tube dependsupon the installation and pressure requirements of the hydrauliccircuit. The minimum sinusoidal amplitude of the wavy body is preferablysubstantially equal to the wall thickness of the tube, and the maximumsinusoidal amplitude is preferably substantially equal to one-half theoutside diameter of the tube. Thus a standard one-half inch tube with awall thickness of .065 of an inch would have a minimum wavy amplitude of.065 of an inch and a maximum wavy amplitude of one-quarter of an inch.In the drawings, the tubes shown in Figures 1 to 4 are formed with aminimum amplitude, namely, at a value substantially equal to the Wallthickness of the tube. The tubes shown in Figures 5 to 14, which areone-quarter of an inch in diameter, are formed with a maximum amplitude,namely, at a value substantially equal to one-half the outside diameterof the tube, or an amplitude of one-eighth of an inch. With a minimumsinusoidal amplitude, the ends of the wavy tube may be inserted directlyinto the tube couplings, as shown in Figure 1. With a maximum sinusoidalamplitude, the ends of the wavy sections are preferably terminated instraight sections, whereby the straight sections may be easily insertedinto the tube couplings. Straight end sections may also be used withwavy body sections of minimum sinusoidal amplitudes to assure easyinsertion of the ends of the tube into the couplings. Wavy tube sectionswith straight ends are shown in Figures 5 to 14. While I haveillustrated my invention with one-quarter and one-half inch tubes, it isto be understood that my invention applies equally well to tubes ofother outside diameters.

The length of each pitch for the sinusoidally formed tube, for theminimum amplitude is preferably in a first range having a lower limitnot less than approximately four times the outside diameter of the tubeand having an upper limit not greater than approximately twice thatamount. This range of values is for all sizes of tube diameters. Thus, aone-half inch outside diameter tube would have a pitch length of twoinches for the lower value of said range and four inches for the uppervalue ofsaid range and a one inch outside diameter tube would have apitch length of four inches for the lower value of said range and eightinches for the upper value of said range. In other words, the ratio ofthe pitch length to the outside diameter of the tube, for minimumamplitude falls in a range of 4 to 8. For maximum amplitude, the pitchrange, which is called second rangeof longitudinal pitch, depends uponthe size of the tube diameters and the extent that the tube wall may besinusoidally bent or stretched without weakening the tube wall. This isparticularly true for sharp bends, because it is essential that thedegree of curvature of the wave be not too great as to weaken or damagethe tube wall structure by making too sharp a bend. I find that for a4-inch tube the lower limit'values of the longitudinal pitch for tubewith maximum sinusoidal amplitude and may not be less than approximately1.375 inches; fora %-inch tube, 2.25 inches; for a /2-inch tube, 3inches; for a fli-inch tube, 3.625 inches; for a A-inch tube, 4.312inches; for a 'Ms-inch tube, 5 inches; for a one-inch tube, 6.5 inches;for a 1% inch tube, 8.25 inches; and for a 1 /2 inch tube, 10.5 inches.For upper limit values of longitudinal pitch for tube with maximumsinusoidal amplitude, the ratio of the pitch l ength to the outsidediameter of the tube is preferably not less than approximately 5.5 for%-iHCh tube; 6.0 for %-inch tube; 6.0 for /2-inch tube; 5.8 for %-inchtube;

5.8 for %-i11Ch tube; 5.8 for Aa-inch tube; 6.5 for oneinch tube; 6.6for 1%-l11Ch tube; and 7.0 for l /z-inch tube. The ratio values givenabove represent the number of times that the pitch is longer than theoutside diameter of the tube. The upper limit values of longitudinalpitch, for maximum amplitudes, are approximately twice the above listedamounts.

For maximum amplitudes, the radius bend of the curvature for the lowerlimit of the second pitch range is approximately W of an inch for a4-inch tube; of an inch for a %-inch tube; 1% inches for a /z-inch tube;1 /2 inches for a /s-inch tube; 1% inches for a 4-inch tube; 2 inchesfor a /s-inch tube; 3 inches for a one-inch tube; 3% inches for a1%--il.10h tube; and 5 inches for a l /z-inch tube. Curvatures withthese radius bends are not too sharp to weaken or damage the wallstructure of the tube.

For the above-mentioned radius bends which are for the lower limit ofthe second pitch range for maximum amplitudes, and which are the mostcritical bends, the ratio of the radius of curvature to the outsidediameter of the tube is as follows: the ratio for fii-inch tube is 2.26;for /s-inch tube is 2.5; for Az-inch tube is 2.5; for /s-inch tube is2.4-; for Ai-inch tube is 2.34; for Az-inch tube is 2.28; for one-inchtube is 3.0; for IMt-inch tube is 3.0; and for l /z-inch tube is 3.33.

Summarizing, the entire pitch range, extending from the lower values ofthe first pitch range for minimum amplitudes to the upper values of thesecond pitch range for the maximum amplitudes, is from 4 to 14 times theoutside diameter of the tube.

For minimum amplitudes and for the lower values of the pitch range, thedeparture angle, which is the included angle between a line drawnsubstantially tangent to the sinusoidal Wave and its longitudinal axis,is in the neighborhood of 10 degrees, see Figure 2. For maximumamplitudes and for the lower values of the pitch range, the

6 departure angle is in the neighborhood of 35 degrees, see Figure 5.

It is to be observed that the'outside wall of the wavy body or tube doesnot dip down sufficiently to cross the longitudinal axis of the tube,the maximum dip touching the horizontal axis. The distance between thebottom of the dip and the horizontal axis may be referred to as anegative internal altitude, meaning that the outside wall does not crossthe longitudinal axis. Thus, in Figure 4, it is noted that for minimumamplitudes, the wavy body has a negative internal altitude which is thespace between the two arrows 20 and 2 1, and which is less than one-halfof the outside diameter of the tube. The value of the negative internalaltitude, for maximum amplitudes, is equal to zero. This is true becausethe amplitude is equal to one-half the outside diameter of the tube, Bykeeping the internal altitude of the wavy body to zero or a negativevalue, the longitudinal rigidity of the tube is assured, in that thewavy tube will not readily elongate or tend to easily unwind, becausethe unwinding eifect which would lengthen the tube is resisted by .themetal of the tubing which is within the central area of the negativeinternal altitude. In other words, by keeping the internal altitude ofthe wavy body to a negative value, the longitudinal straightening effectis resisted, as distinguished from a Wavy body having a positivealtitude whereby the dip goes positive below the horizontal axis.

The effect of forming the tube in a Wavy body having a negative internalaltitude is to give a stiflness or lateral rigidity to the tube beyondthat afforded by the wall thickness alone. Thus, tube lateral vibrationsincident to peak fluid shocks or mechanical shocks are minimized and therequirement for bracing or clamping the tube is eliminated. Accordingly,one benefit derived from making the tube in the form of a wavy body isthat it laterally stifiens the tube to the extent that lateral tubevibrations are minimized, thereby tending to reduce the trouble of theleakage at the couplings. The effect of increasing the rigidity orstiffness of the tube may be appreciated by observing thecross-sectional views in Figure 4, which illustrates the wavy coursetaken by the tubing for one pitch length, the cross-sections being takenat intervals of 45 degrees. Thus, the added rigidity and stiiinessarises from the fact that the effective wall thickness of the tube hasbeen multiplied. This multiplying effect of the rigidity is an importantfeature with respect to insuring long life to the tubing and topreventing hydraulic leakage at the hydraulic fittings. While Figure 4shows the cross-sectional views taken at intervals of 45, it is obvious,of course, that the cross-section of the tube taken at any pointtherealong and normal to the sinusoidal axis is substantially the sameas the cross-section taken at any other point therealong and normal tothe sinusoidal axis.

Another benefit arising from constructing the tube in the form of a wavybody is the fact that the wavy tube may longitudinally give tocompensate for changes in theelongation incident to temperature changesor incident to mechanical vibrations, quiverings or strains, slightlyvarying the spacing between the two hydraulic couplings 14 of thehydraulic units, such as the hydraulic pump 10 and the cylinder 11. Whena non-wavy or straight tubing is employedbetween two spaced connectionpoints, such as between the two couplings 14, it is essential that thelongitudinal strains set up in a straight or non-wavy tube give or berelieved at some point which usually occurs at the connection betweenthe tube and the hydraulic fittings and this relief of the strain orgive at the couplings results in hydraulic leakage. By employing a tubeof my invention, which is of a wavy body, variations in the elongationof the tube compensates for this mechanical strain and thus themechanical and fluid connection between the tube and the hydraulicfittings remains perfect and insures a leak-proof joint. The amount ofthe give which is compensated by the wavy tubular body need be only afew thousandths of an inch, and this amount is adequately taken care ofby making the tube in the form of a wavy body with a negative internalaltitude. Summarizing, my tube, which is of a wavy form with a negativeinternal altitude, is laterally stable or stiff, which eliminates therequirement of clamping the tube to the hydraulic equipment to minimizelateral tube vibrations and is longitudinally stable against easystretching or ready elongation, yet compensating for small variations inlength to relieve mechanical longitudinal strains in the tube whichwould otherwise have to be relieved at the connection between the tubingand the hydraulic fittings which latter condition would destroy thefluid seal.

With maximum amplitudes it is preferable that the short pieces, whichare required for the installation, and which are to be cut oil the longtubes, have straight end sections for insertion in the tube couplings,see Figures to 14. Tubes with minimum amplitudes may also have straightend sections for easy insertion into the tube fittings.

As an alternative method of forming the wavy sections, the short piecesmay be fabricated at the place of the installation by passing theintermediate portion only of a straight short tube through a waveforming machine, thus leaving the end sections straight-to insert intothe tube couplings.

The Figures 5 and 6 comprise an alternate series of straight sections 24and 25 with intermediate wavy sections 22 and 23 therebetween of a totalof two pitch lengths, the amplitude of the wavy sections beingsubstantially equal to one-half the diameter of the tube which has aone-quarter inch outside diameter. The internal altitude issubstantially zero.

The Figures 7 and 8 comprise an alternate series of straight sections 27and 28 with an intermediate wavy section 26 therebetween of one pitchlength. Otherwise the tube shown in Figure 7 is substantially the sameas that shown in Figure 5.

The Figures 9 and 10 comprise an alternate series of straight sections30 and 31 with a one-half pitch section 32 therebetween, the one-halfpitch sections appearing on opposite sides of the longitudinal axis ofthe tube.

The Figures 11 and 12 comprise an alternate series of straight sections35 and 36 with a one-half pitch section 37 therebetween, appearing onthe same side of the longitudinal axis of the tube.

The Figures 13 and 14 comprise an'alternate series of straight sections38 and 39 with an intermediate onequarter pitch section 40. The hollowtube of Figures 13 and 14 thus has at least first and second portionslaterally oifset relative to each other from opposite sides of thelongitudinal axis of the tube, with each of the otfset portions havingcurved end portions 40 and a substantially straight intermediate portiontherebetween.

All the Figures 5 to 14 illustrative a tube having at least two straightpath sections and an intermediate curved path section therebetween, withthe straight path sections adapted for connection to tube fittings. Thecurved path sections deviate from the imaginary longitudinal axis of thetube by an amount equal to or less than one-half the outside diameter ofthe tube and more than the wall thickness of the tube.

The length of the straight end sections may be at least twice the lengthof a coupling nut, plus an additional amount to make it possible to cutoff a short tube of any length from a long tube to accommodateinstallation requirements, and yet have straight end sections to insertinto the tube couplings in longitudinal alignment therewith. Thestraight sections are preferably long enough to be more than adequatefor making right angle bends in the short tube by conventional tubebenders.

For minimum amplitudes it has been found that the small angular approachto the inside of the coupling nut is advantageous, for the reason thatthe wavy tube as it enters the.hole in the back of the nut will contactor touch the internal wall of the hole and thus tend to stop tubevibrations from reaching the point of the connection 7 of the tube andthe connector body within the nut.

The purposes of the tubings shown in Figures 5 to 14 is to illustratethe fact that the wavy body may be combined with straight sectionswhereby for ordinary installation work the operator can utilize thebenefit of the straight sections as localized zones for bending thetubing and as localized zones for easy inserting of the straightsections into the inside of the tube fittings. In all events, theimportance of the wavy body is to increase the lateral stability of thetube against lateral vibrations and to allow the longitudinal length ofthe tube to give a small amount to compensate for the relief oflongitudinal mechanical strains in the tube incident to mechanicalchanges and quiverings of the connected or joined parts of the hydraulicunits between which the tubing runs.

While giving the above desired benefits, the resistance to the flow ofthe fluid through the wavy sections is not appreciably increased, and tothis extent the amplitude should preferably be not made any greater thannecessary.

The sinusoidal tube disclosed and claimed herein is not limited to aperfect sine wave, but the term sinusoidal is used in a generic sense todefine the general shape of the curved tube.

Although this invention has been described in its preferred form with acertain degree of particularity, it is understood that the presentdisclosure of the preferred form has been made only by way of exampleand that numerous changes in the details of construction and thecombination and arrangement of parts may be resorted to withoutdeparting from the spirit and the scope of the invention as hereinafterclaimed.

I claim as my invention:

A sinusoidal bendable tube having its wall bent to conform to a sinusoidresiding within the following range between minimum and maximum limitsof sinusoidal amplitude and of longitudinal pitch, said minimumsinusoidal amplitude being defined as being equal to approximately thesame as the wall thickness of the tube and said maximum sinusoidalamplitude being defined as approximately equal to one-half the outsidediameter of the tube, said minimum longitudinal pitch being equal to 4times the outside diameter of the tube and said maximum longitudinalpitch being 14 times the outside diameter of the tube, the cross-sectionof said tube taken at any point therealong and normal to the sinusoidalaxis being substantially the same as the cross-section taken at anyother point therealong, and normal to said sinusoidal axis.

References Cited in the file of this patent UNITED STATES PATENTS249,547 Reed Nov. 15, 1881 731,124 Park June 16, 1903 811,016 Whyte etal. Jan. 30, 1906 1,315,853 Nordling et al. Sept. 9, 1919 1,535,531Isaachsen Apr. 28, 1925 1,991,788 Cartter Feb. 19, 1935 2,252,045Spanner Aug. 12, 1941 2,587,521 Peterson Feb. 26, 1952 FOREIGN PATENTS21,071 Norway Jan. 30, 1911 486,690 Germany Nov. 22, 1929

